JP-2005-330956A (corresponding to U.S. Pat. No. 7,077,087B2) shows a valve timing controller which includes an electric motor, a drive circuit, and a control circuit. The control circuit generates a control signal according to a rotation direction of an electric motor. The drive circuit energizes the electric motor according to the control signal. A motor rotation signal indicative of a rotation direction of the motor is generated by the driving circuit and is outputted into the control circuit.
In a case that a power source voltage supplied to the drive circuit is dropped, or a break is occurred in a signal line through which a motor rotation signal is transmitted from the driving circuit to the control circuit, it might be possible that the control circuit does not recognize the rotation direction of the electric motor. If the control circuit erroneously recognizes the rotation direction and generates a control signal based on the erroneous rotation direction, it may cause a trouble in operating the engine.